The invention relates to a starter generator for an internal combustion engine and to a method for producing it, as defined by the characteristics recited in claims 1 and 9.
From the prior art, starting systems for internal. combustion engines are known that as a rule comprise a battery-operated DC motor (starter generator) as well as switch gear and control units. For starting the engine, a torque is transmitted by the starter generator. Otto engines in general require rotary speeds of 60-100 rpm, and diesel engines require rotary speeds of approximately 80-200 rpm. In the course of progressive reductions in weight and installation space as well as improvements to the starting power, numerous modifications of the starter system have been developed. For instance, in so-called layshaft starters, by means of one additional gear stage, a total step-up of an armature torque generated by the starter generator can be increased. However, the need still exists to reduce weight and installation space, improve cooling power or recycling capability, and reduce the number of structural elements. Advantageous modifications of the starter generator are therefore desired.
According to the invention, with the aid of the starter generator and the method for producing it having the characteristics recited in independent claims 1 and 9, an especially simple, economical production method on the one hand and a starter generator of reduced weight and installation space that is especially easy to adapt to customer requirements on the other can be made available. The starter generator has a rotor and a stator, whose structural elements substantially comprise stacked, joined-together metal sheets.
According to the method, the metal sheets that form the stator and the rotor are connected to one another by joining. The joining can be done by punch packing, welding, adhesive bonding or riveting. The individual metal sheets are pretreated and stacked on one another in such a way that the essential structural elements of the two components are at least maximally preshaped.
Preferably, the structural elements of the rotor, individually or combined, include a hub, a bearing seat, and a sensor ring for detecting rpm and/or the direction of rotation. If in addition short-circuit bars and/or short-circuit rings are created on the rotor, this can preferably be done by aluminum casting or copper casting.
With a suitable geometry of the metal sheets that form a stator after being joined, in particular such structural elements as a pin bore, a bore pattern and a cooling system can be created directly. In a preferred variant, part of the cooling system is formed by recesses on the outer edge of the stator. The recesses then serve in an ensuing production step to receive cooling tubes. In a preferred feature of such a cooling system, the cooling tubes have knurling on their tube surface, which increases a retention force on a base body of the stator. For permanent fixation to the stator, the cooling tubes can also be press-fitted in it, or can initially merely be placed in the recess of the stator and then widened by means of a mandrel.
Alternatively or in a combination for this purpose, the cooling system can be accommodated in the interior of the stator (internal cooling), or the jacket faces of the cooling system are formed by an external edge of the stator and a gear bell that receives the stator (external cooling). For sealing off the cooling system, a sealing means, such as an electroplated coating, a heat-resistant and coolant-resistant paint, or a synthetic resin can be applied in the region of the jacket faces of the cooling system.
Further preferred features of the invention will become apparent from the other characteristics recited in the dependent claims.